A significant winter storm will lambaste the region Monday night further destabilizing the smorgasbord of weak layers in our upper snowpack. Avoid all avalanche terrain at this time, large to very large natural avalanches are likely as the snowpack adjusts to this new load.
A buried layer of surface hoar is now primed for human triggering. Monday night's storm is certain to add increased vigor to this problem. The slab rests on a persistent weak layer which has the capacity to propagate avalanches across terrain features. Wind exposed features are expected to be particularly volatile.
We're expecting 15 to 35 cm of new snow Monday night into Tuesday with strong north wind. Watch for the formation of fresh sensitive slabs in the new snow that will likely be sensitive to human triggering all day Tuesday.
One last pulse tonight, and then it looks like we’re moving into a bit of a clearing trend this week.
MONDAY NIGHT: Freezing level around 1000 m, strong southwest switching to northwest wind, 10 to 35 cm of snow expected.
TUESDAY: Broken cloud cover, freezing level near valley bottom, moderate northwest wind, 1 to 5 cm of snow possible.
WEDNESDAY: Clear skies, freezing level at valley bottom, light variable wind, no new snow expected.
THURSDAY: Clear skies, freezing level at valley bottom with potential for a light alpine temperature inversion, light southwest to west wind with strong gusts at ridgetop, no new snow expected.
Saturday night's storm resulted in quite a bit of activity. Avalanches to size 2 failed naturally and were sensitive to avalanche control measures Sunday. Reported avalanche activity primarily came from northeast, north and northwest facing features at and above treeline. This MIN highlights that activity nicely.
On Friday and Saturday the buried surface hoar continued to show it's stuff making for touchy avalanche conditions which produced slabs to size 1.5, check out this great MIN report from the north of the region Saturday. Natural wind slabs and cornice failures were reported on alpine features in the central portion of the region to size 1.5.
In the south of the region the snowpack is thin and there have been reports of whumphing at ridgetop. Check out all of the MIN reports for the region here
30 to 75 cm of storm snow has fallen recently with the deepest amounts being found in the north around Golden. Southwest winds have built slabs in lee features at upper elevations, reactive cornices have grown too.
Below the storm snow, the snowpack is a bit of a junk show. The early December surface hoar is down 30 to 80 cm below the surface now. On Saturday, before the big storm, it was sensitive to remote triggering which is well illustrated in this MIN post from the Golden area.
Below, or near the surface hoar you may encounter a crust. This crust can be bound as high as 2400 m in the south of the region and 1800 m in the north.
The lower snowpack is characterized by more crusts, the most notable is from a rain event in early November that is 50 to 130 cm deep. This crust is sitting near the base of the snowpack, surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers or in a step-down from a smaller avalanche in shallow, rocky areas.
